1. Field
Embodiments of the present inventive concept relate to a cassette transfer apparatus, which may be configured to transfer a cassette that has wafers loaded therein by stably supporting the cassette, and a cassette transferring method using the same.
2. Description of the Related Art
A semiconductor product is manufactured by forming a predetermined integrated circuit on a wafer. In semiconductor product manufacturing, a single wafer is subjected to multiple processes including a first diffusion process to allow an oxide layer to grow on a wafer, an impurity implantation process and a second diffusion process to implant an impurity and to diffuse the implanted impurity into a silicon wafer to a desired depth, a photolithography process to form a mask (or a reticle) pattern on the wafer to selectively define a portion to be protected from etching or ion implantation, an etching process to selectively remove, using an etching gas or a chemical, thin films grown or deposited on a predetermined portion of the wafer, and a thin film forming process to form, using chemical vapor deposition, ion implantation, or metal deposition, a particular film.
In each of the processes, multiple unit process steps may be performed. For example, in the photolithography process, several unit process steps, including a coating of a photoresist step, a developing step, a baking step, an exposing step, and so on, are performed. In the coating of the photoresist step, the photoresist is coated on a wafer. In the developing step, a photoresist layer, formed on a predetermined portion of a surface of the wafer, which has undergone mask alignment and exposure, is removed using a developer solution to separately form a necessary portion and an unnecessary portion of the wafer. In the baking step, the wafer, which has been coated with the photoresist by a spin coater, is heated and then cooled to increase adhesion between the photoresist and the wafer surface. In the exposing step, using an optical lens, the mask pattern is reduced and exposed and configured to be transferred onto the wafer.
In order to increase product yields, multiple processing tools of each of various processing devices configured to perform the unit process steps are provided in each process bay and operated. Loading and unloading wafers from one processing device to another are conducted in units of lots (i.e., cassettes with 20 to 25 wafers) to be conveyed between processing devices. The lot unit wafers are mounted on a cassette and transferred by a cassette transfer apparatus from the processing devices in each process bay.